Field of the Invention
This invention relates to condensates of aliphatic aldehydes and ketones with amino containing reactants. More particularly, this invention relates to a series of hydrolytically stable, water soluble Schiff bases. This group of Schiff bases is useful as surface active agents.
The term surfactant refers to substances which lower liquid-liquid, liquid-solid or liquid-gas interfacial tension. Surfactant solutions used by themselves or in conjunction with cleaning adjuvants such as additives or builders are widely used to wet surfaces, remove soil, penetrate porous materials, disperse particles, emulsify oils and greases, etc., dependent upon the particular characteristics of the surfactant or surfactants used.
Desirably surfactants are inexpensive, light colored materials which function at low concentration levels in aqueous solutions and which can be produced in good yield from readily available low cost starting materials, free from deleterious contaminants, preferably as easily handled, free-flowing liquids or powders.
For many applications, such as heavy duty industrial applications for metal scouring and dishwasher detergent compositions, the compositions necessarily include highly alkaline materials such as alkali metal hydroxides, alkoxides and phosphates. In the aqueous media that these detergents function, the pH of the cleaning solution frequently will be from 10 to 13. For this reason a prerequisite of heavy duty detergency compositions is stability at elevated pH's in aqueous solutions.
Solubilized Schiff bases derived from the condensation of aliphatic ketones with amine-containing reactants are particularly of interest in view of the disclosure of British Pat. No. 414,712 (1933) which states that solubilized (ethoxylated or sulfonated, etc.) Schiff bases prepared by condensing aliphatic aldehydes or ketones of more than 6 carbon atoms with aliphatic amines or amino alcohols produce high foaming detergents stable to hard (alkaline) water. Unfortunately solubilized condensation products as exemplified by the ethoxylated condensate of Schiff bases prepared from the reaction of C.sub.11 -C.sub.13 ketone mixtures or methyl nonyl ketone with amino-containing reactants such as ethanolamine are extremely unstable in aqueous solutions ranging from pH 5.6 to 13. Inasmuch as this pH range includes most cleaning applications, the unstabilized condensate products of the British Patent are practically of no value as detergent components.
U.S. Pat. No. 3,897,362 (1975) McCoy, describes a series of Schiff base surfactants which are more stable than those of British Pat. No. 414,712 but significantly less hydrolytically stable than the Schiff bases of the present invention as shown in Example VIII.